Generally, an expanded grid used as the core of an electrode of a storage battery is manufactured in a step of forming parallel intermittent cuts in the width direction in a surface of a region excluding the central portion of a thin plate in a band form made of metal such as lead or lead alloy continuously in a zigzag form, and a step of expanding and developing the thin plate having cuts in the width direction. The expanded grid used widely as the grid for electrode plates of a lead acid storage battery is superior to the casting grid in the mass producibility, and is suited to the lead acid storage batteries of mass-produced automobiles. Recently, a higher performance is demanded in the batteries, and it is required to reduce the mesh size of the grid in order to enhance the current collecting effect of the grid.
However, in such an expanded grid, the width is developed by extending the cuts sequentially. As a result, the track distance at the outermost side of the band metal plate is longer than the track distance in the central portion. Accordingly, creases are formed when developing the thin plate having cuts in a flat plane, and the creases cause deflection, which yield periodic creases in the developed grid. Due to such creases, the width dimension of the grid becomes unstable. As a result, adjusting the manufacturing condition becomes a labor-intensive task. Furthermore, the dimensional precision of the electrode plate is not stable, and the quality fluctuations are significant. In addition, a local distortion occurs in the grid which is likely to promote grid corrosion. Such phenomenon occurrs more prominently in the grid with the smaller mesh size.